The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 369 2014 February 2
Here is the latest round-up of news from the Society for Popular
Astronomy. The SPA is Britain's liveliest astronomical society, with
members all over the world. We accept subscription payments on-line
at our secure site and can take credit and debit cards. You can join
or renew via a secure server, or just see how much we have to offer by
visiting http://www.popastro.com/ WATER DETECTED ON DWARF PLANET CERES
NASA The spacecraft called Dawn, which has spent more than a year orbiting
the large asteroid Vesta, is now on its way to Ceres, where it is
scheduled to arrive in the spring of 2015. For more than a century,
Ceres was known as the largest asteroid in the Solar System, but in
2006 the International Astronomical Union, the governing organization
responsible for naming planetary objects, re-classified it as a 'dwarf
planet' because of its large size -- it is roughly 950 km in diameter.
(But it is still an asteroid, for all that!) When it was discovered
in 1801, astronomers thought that it was a planet orbiting between
Mars and Jupiter. Later, other cosmic bodies with similar orbits were
found, marking the discovery of the Solar System's main belt of
asteroids. Scientists think that Ceres contains rock in its interior,
with a thick mantle of ice that, if melted, would amount to more fresh
water than exists on the Earth. The materials making up Ceres
probably date from the first few million years of the Solar System's
existence and accumulated before the planets formed. Scientists using the Herschel infrared space observatory have recently
detected water vapour on Ceres. It appears that plumes of water
vapour shoot up when portions of its icy surface warm slightly.
Until now, ice had been thought to exist on Ceres but had not been
detected conclusively. Herschel did not see water vapour every time
it looked: although it observed water vapour four different times, on
one occasion there was no such signature. Scientists think that, when
Ceres is in the part of its orbit that is closest to the Sun, some of
its icy surface becomes warm enough to cause water vapour to escape in
plumes at a rate of about 6 kilograms per second, while in the colder
part of its orbit no water escapes. The strength of the signal also
varied over hours, weeks and months, because of the water-vapour
plumes rotating in and out of Herschel's view as Ceres spun on its
axis. That enabled the scientists to localize the sources of water to
two dark spots on the surface of Ceres, previously seen by the Hubble
Space Telescope and ground-based telescopes. The dark spots might be
more likely to outgas because dark material absorbs heat better than
light material. When Dawn arrives, we can hope to learn a lot more.
MILKY WAY MAY HAVE FORMED OUTWARDS FROM THE INSIDE
University of Cambridge Observations of the chemical composition of stars in the Milky Way's
disc, particularly, in the study reported here, the fast-produced
element magnesium, allow astronomers to estimate how rapidly different
parts of the Milky Way were formed. The research suggests that stars
in the inner regions of the Galactic disc were the first to form,
supporting ideas that our Galaxy grew from the inside out. Using data
from the 'Very Large Telescope' in Chile, an international team of
astronomers observed stars with a wide range of ages and locations to
determine their 'metallicity' -- the amount of chemical elements in a
star other than hydrogen and helium, the two dominant elements.
Immediately after the Big Bang, the Universe consisted almost entirely
of hydrogen and helium, with levels of metallic elements growing over
time. Consequently, older stars in general have lower metallicities.
The different chemical elements are created at different rates -- some
in massive stars which live fast and die young, and others in Sun-like
stars with more sedate multi-billion-year lifetimes. Massive stars,
which have short lives and die as 'core-collapse supernovae', produce
huge amounts of magnesium when they explode. The team has shown that
older, 'metal-poor' stars inside the Solar Circle -- the orbit of the
Sun around the centre of the Milky Way, which takes roughly 250
million years to complete -- are far more likely to have high levels
of magnesium than those outside. The higher levels of the element
inside the Solar Circle suggest that that area contained more stars
that 'lived fast and died young' in the past. The stars that lie
outside the Solar Circle are predominantly younger, both 'metal-rich'
and 'metal-poor', and have surprisingly low magnesium levels compared
to their general metallicity. That observation may signify important differences in stellar
evolution across the Milky Way's disc, with short star-formation
time-scales occurring inside the Solar Circle whereas outside the
Sun's orbit star-formation took much longer. That supports certain
theoretical models for the formation of disc galaxies, which predict
that galactic discs grow from the inside out. The new research also
bears on an apparent 'double structure' in the Milky Way's disc -- the
so-called 'thin' and 'thick' discs. The thin disc hosts spiral arms,
young stars, giant molecular clouds -- all objects which are young, at
least in the context of the Galaxy. But astronomers have suspected
that there is another disc, which is thicker, shorter and older, and
has many old stars that have low metallicity. In the new research,
the team found that stars in the young, 'thin' disc aged between 0 and
8 billion years all have a similar degree of metallicity, regardless
of age in that range, with many of them considered 'metal-rich'. Then
there is a steep decline in metallicity for stars aged over 9 billion
years, typical of the 'thick' disc, with no detectable 'metal-rich'
stars found at all over that age. But stars of different ages and
metallicity can be found in both discs; there is no clear separation
between the thin and thick discs. The proportion of stars with
different properties is not the same in both discs -- that's why we
think that the two discs probably exist -- but they could have very
different origins. The study provides evidence that the inner parts
of the Milky Way's thick disc formed much more rapidly than did the
thin-disc stars, which dominate in our neighbourhood.
DISTANT QUASAR ILLUMINATES FILAMENT OF THE 'COSMIC WEB'
University of California - Santa Cruz Astronomers have discovered a distant quasar illuminating a vast
nebula of diffuse gas, revealing for the first time part of the
network of filaments thought to connect galaxies in a 'cosmic web'.
Using the 10-m Keck I telescope in Hawaii, the researchers detected a
gaseous nebula extending about 2 million light-years across
intergalactic space. It is an exceptional object, at least twice as
large as any nebula detected before, and it extends well beyond the
galactic environment of the quasar. The standard cosmological model
of structure formation in the Universe would like galaxies to be
embedded in a cosmic web of matter, most of which (about 84%) is
invisible dark matter. The web appears in the results from computer
simulations of the evolution of structure in the Universe, which show
the distribution of dark matter on large scales, including the
dark-matter haloes in which galaxies form and the cosmic web of
filaments that connect them. Gravity causes ordinary matter to follow
the distribution of dark matter, so filaments of diffuse, ionized gas
are expected to trace a pattern similar to that seen in dark-matter
simulations. Until now, however, such filaments have never been seen.
Intergalactic gas has been detected by its absorption of light from
bright background sources, but those results do not show how the gas
is distributed. In this study, the researchers detected the
fluorescent glow of hydrogen gas resulting from its illumination by
intense radiation from the quasar. The quasar is illuminating diffuse
gas on scales beyond any seen before, giving us the first picture of
extended gas between galaxies. If the cosmic web is as ubiquitous as
some theoreticians would have us believe, however, it seems strange
that, with all the interest that there has been in quasars, none of
them has ever seemed to have illuminated such material before. The hydrogen gas illuminated by the quasar emits far-ultraviolet light
known as Lyman-alpha radiation. The distance to the quasar is so
great (about 10 billion light-years) that the wavelength of the
emitted light is red-shifted by the expansion of the Universe into the
observable spectrum by the time it reaches here. The researchers
imaged the quasar through a filter that passed just the light that had
started out at the Lyman-alpha wavelength. The light from the quasar
is like a torch beam, and in this case they were lucky that the beam
is pointing towards the nebula and making the gas glow. It has been
suggested that the nebula may be even bigger than it appears, but we
only see the part of the filament that is illuminated by the beamed
emission from the quasar.
INVENTOR OF THE POPULAR DOBSONIAN TELESCOPE DIES AT 98
Universe Today John Dobson, famous as the creator of the simple, low-cost Dobsonian
telescope, passed away on 2014 Jan. 15 at the age of 98. Dobson was
born in Beijing, but moved with his parents to San Francisco in 1927.
After spending 23 years in a monastery, some of which time was spent
sneaking out to build telescopes and observe the night sky, he left
to co-found the San Francisco Sidewalk Astronomers in 1968, a group
dedicated to showing people on the street the wonders of the night sky
using what were (for the time) large telescopes. Dobson's interest in astronomy started in the early 1950s when he
built a small telescope from parts obtained from a junk shop. He
wanted to see for himself what the Universe looked like. By 1956, he
got hold of a 12-inch slab of porthole glass and ground it into a
mirror following instructions from Allyn J. Thompson's classic book
'Making Your Own Telescope'. Dobson shook up the amateur telescope-
making universe with an innovative design based on simplicity. Most
telescopes of his day were small refracting telescopes or small to
modest-sized reflectors with metal tubes and heavy equatorial mounts.
Neither was exactly user-friendly nor offered much light. John used
simple materials like porthole glass, cardboard tubes and wooden
altitude-azimuth mounts to build large telescopes that were incredibly
easy to use. While such mounts were nothing new, Dobson combined
cheap materials, large mirrors and a simpler approach to mountings
that made his telescope style unique.
SPA SOLAR SECTION November 2013
By Geoff Elston, SPA Solar Section Director The combination of short days, low Sun, and frequently cloudy
weather tested the patience of many of us in November. Despite the
difficulties, between us we observed the Sun on all but two days in
the month. For those who were blessed with clear skies and steady air
there was plenty to see and image in white light and H-alpha. Rotation Nos. 2143 and 2144: The Mean Daily Frequency remained nearly
level, slightly up from 5.10 in October to 5.26. The Relative Sunspot
Number also rose slightly from 71.65 in October to 80.47 in November. WHITE-LIGHT ACTIVITY: At the beginning of November all sunspot
activity appeared in a long line along the southern hemisphere of the
solar disc. AR 1884 and AR 1885 (a grouping of sunspots that
resembled the Southern Cross in the southern night sky) was just past
the Central Meridian (CM). AR 1882 and AR 1888 were approaching the
west. A fairly large group, AR 1890, appeared over the SE limb on the
3rd. It was not visible to the naked eye at first, but as it crossed
the disc it became visible to the protected naked eye on the 8th and
9th. It showed a very complex structure and on the 11th I noticed
that the leader spot had several umbrae and a mixture of spots and
fragments of penumbrae following the leader. As AR 1890, which by then was decaying, neared the western limb, the
12th saw some more sunspot activity near the SE limb particularly
AR 1895 and 1897, which appeared as a long fragmented grouping of
sunspots with many umbrae and numerous pores. AR 1899, a large single
spot, appeared foreshortened as it was very close to the E limb. It
was preceded by AR 1896, a single spot. AR 1899 was visible to the
naked eye from the 15th to the 22nd, probably because it was a single
large sunspot. As it neared the W limb sunspot activity declined,
leaving AR 1903 at the CM on the 23rd. There were few observations
for the last week of November but it seems that sunspot activity was
at a low level until the 27th when more sunspots appeared over the E
limb. H-ALPHA ACTIVITY: A tall complex prominence was very clearly seen on
the W limb on the 1st, as were a slightly smaller hedgerow near the S
limb and some detached cloud-like prominences on the NE limb.
Filaments and plages were seen near to the highly active AR 1882,
1884 and 1885 as well as near the SE limb. The 4th was very active
with plenty of dark filaments and bright plages all across the disc.
There were also some very nice spike prominences along the limb but
especially on the east where there was a impressive hedgerow-type
prominence. By the 9th and 10th, with AR 1890 near the CM, that
region was bright with plage activity. There were several dark
filaments elsewhere across the solar disc, and prominences on the S
and W limbs and particularly the NE limb where some tall ones were on
show. A Section member reported on the 12th that he had imaged a bright-
edged prominence on the E limb associated with AR 1899 that almost
resembled a flare. There were also some really nice prominences around
the solar limb, particularly one on the SE limb that showed fragmented
arches within it, a very active NW limb, and a bright detached one
that was clear of the W limb. Filament and plage activity associated
with AR 1893, 95, 96 and 99 continued to dominate from the 14th
onwards as they crossed the disc. On the 19th an extensive hedgerow
prominence was seen on the NW limb, some of it near to sunspot group
AR 1893. MDF (P): 7.84 Go to the Solar Section link on the SPA homepage to see a selection of
the many remarkable images and drawings made by the Section membership.
Bulletin compiled by Clive Down (c) 2014 the Society for Popular Astronomy |
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